Process of fabricating lateral mode capacitive microphone

ABSTRACT

The present invention provides a process of fabricating a capacitive microphone such as a MEMS microphone. In the process, one electrically conductive layer is deposited on a removable layer, and then divided or cut into two divided layers, both of which remain in contact with the removable layer as they were. One of the two divided layers will become or include a movable or deflectable membrane/diaphragm that moves in a lateral manner relative to another layer, instead of moving toward/from another layer. A motional sensor is optionally fabricated within the microphone to estimate the noise introduced from acceleration or vibration of the microphone for the purpose of compensating the microphone output through a signal subtraction operation.

CROSS-REFERENCE TO RELATED U.S. APPLICATIONS

This application is a Continuation-in-Part of U.S. non-provisionalapplication Ser. No. 15/623,339 filed on Jun. 14, 2017, which isContinuation-in-Part of U.S. non-provisional application Ser. No.15/393,831 filed on Dec. 29, 2016, both of which are incorporated hereinby reference in their entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

NAMES OF PARTIES TO A JOINT RESEARCH AGREEMENT

Not applicable.

REFERENCE TO AN APPENDIX SUBMITTED ON COMPACT DISC

Not applicable.

FIELD OF THE INVENTION

The present invention generally relates to a process of fabricating alateral mode capacitive microphone. The microphone of the invention mayfind applications in smart phones, telephones, hearing aids, publicaddress systems for concert halls and public events, motion pictureproduction, live and recorded audio engineering, two-way radios,megaphones, radio and television broadcasting, and in computers forrecording voice, speech recognition, VoIP, and for non-acoustic purposessuch as ultrasonic sensors or knock sensors, among others.

BACKGROUND OF THE INVENTION

FIG. 1A is a schematic diagram of parallel capacitive microphone in theprior art. Two thin layers 101 and 102 are placed closely in almostparallel. One of them is fixed backplate 101, and the other one ismovable/deflectable membrane/diaphragm 102, which can be moved or drivenby sound pressure. Diaphragm 102 acts as one plate of a capacitor, andthe vibrations thereof produce changes in the distance between twolayers 101 and 102, and changes in the mutual capacitance therebetween.

“Squeeze film” and “squeezed film” refer to a type of hydraulic orpneumatic damper for damping vibratory motion of a moving component withrespect to a fixed component. Squeezed film damping occurs when themoving component is moving perpendicular and in close proximity to thesurface of the fixed component (e.g., between approximately 2 and 50micrometers). The squeezed film effect results from compressing andexpanding the fluid (e.g., a gas or liquid) trapped in the space betweenthe moving plate and the solid surface. The fluid has a high resistance,and damps the motion of the moving component as the fluid flows throughthe space between the moving plate and the solid surface.

In capacitive microphones as shown in FIG. 1A, squeeze film dampingoccurs when two layers 101 and 102 are in close proximity to each otherwith air disposed between them. The layers 101 and 102 are positioned soclose together (e.g. within 5 μm) that air can be “squeezed” and“stretched” to slow movement of membrane/diaphragm 102. As the gapbetween layers 101 and 102 shrinks, air must flow out of that region.The flow viscosity of air, therefore, gives rise to a force that resiststhe motion of moving membrane/diaphragm 101. Squeeze film damping issignificant when membrane/diaphragm 101 has a large surface area to gaplength ratio. Such squeeze film damping between the two layers 101 and102 becomes a mechanical noise source, which is the dominating factoramong all noise sources in the entire microphone structure.

Co-pending U.S. application Ser. No. 15/393,831 to the same assignee,which is incorporated herein by reference, teaches a so-called lateralmode microphone in which the movable membrane/diaphragm does not moveinto the fixed backplate, and the squeeze film damping is substantiallyavoided. An embodiment of the lateral mode microphone is shown in FIG.1B. First electrical conductor 201 is stationary, and has a functionsimilar to the fixed backplate in the prior art. A large flat area ofsecond electrical conductor 202, similar to movable/deflectablemembrane/diaphragm 102 in FIG. 1A, receives acoustic pressure and movesup and down along the primary direction, which is perpendicular to theflat area. However, conductors 201 and 202 are configured in aside-by-side spatial relationship, not one above another. As one “plate”of the capacitor, conductor 202 does not move toward and from conductor201. Instead, conductor 202 laterally moves over, or “glides” over,conductor 201, producing changes in the overlapped area between 201 and202, and therefore varying the mutual capacitance therebetween. Acapacitive microphone based on such a relative movement betweenconductors 201 and 202 is called lateral mode capacitive microphone.

An acceleration of the lateral mode capacitive microphone may affect theaccuracy of sound detection. An acceleration of 1G on the direction thatis normal to the flat area of conductor 202 (or membrane 202) causes asignal to be detected, whose value may be 13% of 1 Pa sound pressure.Signal to Acceleration Ratio (SAR) may be used to define this effect.For example, the SAR for a single slot design structure disclosed in theco-pending U.S. application Ser. No. 15/393,831 can be around 7.6, whichis much smaller than the typical SAR 70-100 for a conventional MEMSmicrophone. A microphone with low SAR will suffer from inaccurate signaldetection when the microphone vibrates at low frequency. For example, ifthe microphone, or a device using such a microphone (e.g. a cellphone),is being used in a running automobile, the shake or vibration of thedevice along the automobile is actually an acceleration applied onmembrane 202 and may be “misread” as a sound signal.

Co-pending U.S. application Ser. No. 15/623,339 to the same assignee,which is incorporated herein by reference, teaches a motional sensorthat is used in the microphone to estimate the noise introduced fromacceleration or vibration of the microphone for the purpose ofcompensating the microphone output through a signal subtractionoperation. In an embodiment, the motional sensor is identical to thelateral microphone, except that the movable membrane in the motionalsensor has air ventilation holes for lowering the movable membrane's airresistance, and making the movable membrane responsive only toacceleration or vibration of the microphone. FIG. 1C illustrates acapacitive microphone 200 such as a MEMS microphone. Microphone 200includes a functional device 290 (or a working capacitive microphone290), and a motional sensor 300. In functional device 290, a firstelectrical working conductor 201 and a second electrical workingconductor 202 are configured to have a relative spatial relationshiptherebetween so that a mutual capacitance can exist between them. Therelative spatial relationship as well as the mutual capacitance can bothbe varied by an acoustic pressure impacting upon conductors 201 and/or202.

FIG. 1D schematically illustrates an exemplary motional sensor 300 inthe lateral mode capacitive microphone 200. Motional sensor 300 isalmost identical to working capacitive microphone 290 as shown in FIG.1C. By “almost identical”, it means that the only difference betweendevice 290 and sensor 300 is that the resistance R_(fd) of conductor 201and/or conductor 202 against an impacting acoustic pressure is muchgreater than the resistance R_(ms) of the counterparts of conductor 201r and/or conductor 202 r in motional sensor 300 against the sameimpacting acoustic pressure. Movable/deflectable membrane/diaphragm 202r, or reference conductor/membrane 202 r, has less air resistance thanthe working membrane 202. For example, reference membrane 202 r may haveone or more openings 288 thereon for air ventilation and reducing airresistance, while working membrane 202 has no such opening(s) or hasless opening(s). As a result, reference membrane 202 r receives littleacoustic pressure, and moves up and down mainly or entirely in responseto the acceleration or vibration of the microphone 200.

In the present invention, a simple and effective process of fabricatinga lateral microphone such as a MEMS microphone as described above isprovided.

SUMMARY OF THE INVENTION

In various embodiments of the invention, the process fabricating thelateral microphone includes the following steps: (A10) providing aworking substrate having a planar working surface, wherein a primaryworking direction is defined as a direction perpendicular to the planarworking surface; (B10) depositing at least one removable layer such as asacrificial layer on the planar working surface; (C10) depositing oneelectrically conductive working layer on said at least one removablelayer, (D10) dividing the electrically conductive working layer into twodivided working layers, both of which remain in contact with said atleast one removable layer and are parallel with the planar workingsurface; and (E10) etching away said at least one removable layer toform a working capacitive microphone. As a result, the capacitivemicrophone includes at least a working capacitive microphone. In someembodiments the process further comprises fabricating a motional sensorhaving no or a minimal response to an acoustic pressure impacting thecapacitive microphone. As a result, the capacitive microphone includesnot only a working capacitive microphone, but also a motional sensor.

The above features and advantages and other features and advantages ofthe present invention are readily apparent from the following detaileddescription of the best modes for carrying out the invention when takenin connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The present invention is illustrated by way of example, and not by wayof limitation, in the figures of the accompanying drawings and in whichlike reference numerals refer to similar elements. All the figures areschematic and generally only show parts which are necessary in order toelucidate the invention. For simplicity and clarity of illustration,elements shown in the figures and discussed below have not necessarilybeen drawn to scale. Well-known structures and devices are shown insimplified form in order to avoid unnecessarily obscuring the presentinvention. Other parts may be omitted or merely suggested.

FIG. 1A shows a conventional capacitive microphone in the prior art.

FIG. 1B illustrates a lateral mode capacitive microphone in a co-pendingU.S. application filed by the same Applicants.

FIG. 1C illustrates another lateral mode capacitive microphone in aco-pending U.S. application filed by the same Applicants.

FIG. 1D illustrates an exemplary motional sensor in the lateral modecapacitive microphone of FIG. 1C.

FIG. 2 schematically illustrates some steps in a process of fabricatinga capacitive microphone such as a MEMS microphone in accordance with anexemplary embodiment of the present invention.

FIG. 3 schematically illustrates some steps in a process of fabricatinga capacitive microphone such as a MEMS microphone in accordance with anexemplary embodiment of the present invention.

FIG. 4A schematically illustrates some steps in a process of fabricatinga capacitive microphone in accordance with an exemplary embodiment ofthe present invention.

FIG. 4B schematically illustrates a step in a process of fabricating acapacitive microphone in accordance with an exemplary embodiment of thepresent invention.

FIG. 4C schematically illustrates a step in a process of fabricating acapacitive microphone in accordance with an exemplary embodiment of thepresent invention.

FIG. 4D schematically illustrates a step in a process of fabricating acapacitive microphone in accordance with an exemplary embodiment of thepresent invention.

FIG. 5A schematically shows a MEMS capacitive microphone in accordancewith an exemplary embodiment of the present invention.

FIG. 5B schematically shows a MEMS capacitive microphone in accordancewith an exemplary embodiment of the present invention.

FIG. 6 illustrates the first/second working electrical conductors havinga comb finger configuration in accordance with an exemplary embodimentof the present invention.

FIG. 7 depicts the spatial relationship between two working comb fingersof FIG. 6 in accordance with an exemplary embodiment of the presentinvention.

FIG. 8A illustrates a working capacitive microphone including fouridentical movable working membranes arranged in a 2×2 arrayconfiguration in a co-pending U.S. application filed by the sameApplicants.

FIG. 8B shows a capacitive microphone including one movable referencemembrane and three movable working membranes arranged in a 2×2 arrayconfiguration in accordance with an exemplary embodiment of the presentinvention.

FIG. 8C shows a capacitive microphone including two movable referencemembranes and two movable working membranes arranged in a 2×2 arrayconfiguration in accordance with an exemplary embodiment of the presentinvention.

FIG. 8D shows another capacitive microphone including two movablereference membranes and two movable working membranes arranged in a 2×2array configuration in accordance with an exemplary embodiment of thepresent invention.

FIG. 9 demonstrates the design of one or more such as two air flowrestrictors in accordance with an exemplary embodiment of the presentinvention.

FIG. 10 illustrates that 4 single dies are arranged as an array devicesuperimposed with the equivalent circuit thereof in accordance with anexemplary embodiment of the present invention.

FIG. 11 illustrates the configuration of comb fingers, membrane andsuspensions in accordance with an exemplary embodiment of the presentinvention.

FIG. 12 schematically illustrates a suspension spring with folded andsymmetrical cantilevers in accordance with an exemplary embodiment ofthe present invention.

FIG. 13 illustrates the texture representation of six materials anddiagram of several views appeared in the processes of FIGS. 14-36C2 inaccordance with an exemplary embodiment of the present invention.

Regarding FIGS. 14-28, FIG. 14 shows a step of providing aworking/reference substrate.

FIG. 15 illustrates deep reactive ion etching (DRIE) on the substrate.

FIG. 16 illustrates the step of depositing at least one removable layer(such as silicon dioxide) on the substrate.

FIG. 17 illustrates the step of etching a silicon dioxide layer.

FIG. 18 illustrates a step of polysilicon deposition.

FIG. 19 illustrates a step of etching and patterning a polysiliconlayer.

FIG. 20 illustrates a step of 3 μm PSG deposition.

FIG. 21 illustrates a step of etching PSG, and patterning PSG.

FIG. 22 illustrates a step of siliconnitride deposition.

FIG. 23 illustrates a step of patterning the siliconnitride layer.

FIG. 24 illustrates a step of 3 μm polysilicon deposition.

FIG. 25 illustrates a step of etching polysilicon, and patterningpolysilicon.

FIG. 26 illustrates a step of 3 μm PSG deposition.

FIG. 27 illustrates a step of etching/patterning PSG.

FIG. 28 illustrates a step of 1 μm polysilicon deposition as membranematerial.

Regarding FIGS. 29A-32B, FIG. 29A illustrates a step of etchingadditional polysilicon without an opening (or membrane hole) formation.FIG. 29B illustrates a step of etching additional polysilicon with anopening formation. FIG. 30A illustrates a step of depositing metal forpad material. FIG. 30B illustrates a step of depositing metal for padmaterial. FIG. 31A illustrates a step of patterning pads. FIG. 31Billustrate a step of patterning pads. FIG. 32A illustrates a step ofremoving remaining PSG above polysilicon and preparing comb fingersfabrication. FIG. 32B illustrates a step of removing remaining PSG abovepolysilicon and preparing comb fingers fabrication.

Regarding FIGS. 33A1-33C2, FIG. 33A1 illustrates a step ofpatterning/etching polysilicon with no membrane hole. FIG. 33A2illustrates a step of patterning/etching polysilicon with no membranehole. FIG. 33B1 illustrates a step of patterning/etching polysiliconwith a membrane hole. FIG. 33B2 illustrates a step of patterning/etchingpolysilicon with a membrane hole. FIG. 33C illustrates a step ofpatterning/etching polysilicon with a membrane hole. FIG. 33C2illustrates a step of patterning/etching polysilicon with a membranehole.

Regarding FIGS. 34A1-34C2, FIG. 34A1 illustrates a step of etchingsilicon nitride (with no membrane hole). FIG. 34A2 illustrates a step ofetching silicon nitride (with no membrane hole). FIG. 34B1 illustrates astep of etching silicon nitride (with a membrane hole). FIG. 34B2illustrates a step of etching silicon nitride (with a membrane hole).FIG. 34C1 illustrates a step of etching silicon nitride (with a membranehole). FIG. 34C2 illustrates a step of etching silicon nitride (with amembrane hole).

Regarding FIGS. 35A1-35C2, FIG. 35A1 illustrates a step of etching backhole or cavity (with no membrane hole). FIG. 35A2 illustrates a step ofetching back hole or cavity (with no membrane hole). FIG. 35B1illustrates a step of etching back hole or cavity (with a membranehole). FIG. 35B2 illustrates a step of etching back hole or cavity (witha membrane hole). FIG. 35C1 illustrates a step of etching back hole orcavity (with a membrane hole). FIG. 35C2 illustrates a step of etchingback hole or cavity (with a membrane hole).

Regarding FIGS. 36A1-36C2, FIG. 36A1 illustrates a step of removingsacrificial materials (with no membrane hole). FIG. 36A2 illustrates astep of removing sacrificial materials (with no membrane hole). FIG.36B1 illustrates a step of removing sacrificial materials (with amembrane hole). FIG. 36B2 illustrates a step of removing sacrificialmaterials (with a membrane hole). FIG. 36C1 illustrates a step ofremoving sacrificial materials (with a membrane hole). FIG. 36C2illustrates a step of removing sacrificial materials (with a membranehole).

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

In the following description, for the purposes of explanation, numerousspecific details are set forth in order to provide a thoroughunderstanding of the present invention. It is apparent, however, to oneskilled in the art that the present invention may be practiced withoutthese specific details or with an equivalent arrangement.

Where a numerical range is disclosed herein, unless otherwise specified,such range is continuous, inclusive of both the minimum and maximumvalues of the range as well as every value between such minimum andmaximum values. Still further, where a range refers to integers, onlythe integers from the minimum value to and including the maximum valueof such range are included. In addition, where multiple ranges areprovided to describe a feature or characteristic, such ranges can becombined.

Steps (A10)-(E10) are schematically illustrated in FIG. 2 and FIG. 3. Instep (A10), a working substrate having a planar working surface isprovided. The working substrate may be made of silicon. A primaryworking direction is defined as a direction perpendicular to the planarworking surface. In step (B10), at least one removable layer isdeposited on the planar working surface. The removable layer maycomprise PSG or thermal oxide such as oxides of Si. In step (C10), oneelectrically conductive working layer is deposited on the removablelayer. The electrically conductive working layer may comprisepolysilicon, silicon, gold, silver, nickel, aluminum, copper, chromium,titanium, tungsten, or platinum.

In step (D10) as shown in FIG. 3, the electrically conductive workinglayer is divided or cut (e.g. by pattering and etching) into two dividedworking layers, both of which remain in contact with said at least oneremovable layer. Both layers are substantially parallel to the planarworking surface. In step (E10), the removable layer is removed or etchedaway to form a working capacitive microphone.

In steps (D10) and (E10), the two divided working layers become a firstelectrical working conductor and a second electrical working conductorin the working capacitive microphone, as shown in FIG. 3. A mutualcapacitance exists between said two working conductors. The firstelectrical working conductor has a first working projection along saidprimary working direction on the planar working surface, and the secondelectrical working conductor has a second working projection along saidprimary working direction on the planar working surface. The firstworking projection and the second working projection have a shortestworking distance Dwmin therebetween, and Dwmin remains greater than zeroregardless of that one or two of said two working conductors is (are)impacted by an acoustic pressure along said primary working direction ornot. In an embodiment, the electrically conductive working layer has atotal area of A that is in contact with the removable layer after step(C10), but before step (D10). After step (D10), the first electricalworking conductor has a total area of A1 in contact with the removablelayer, and the second electrical working conductor has a total area ofA2 in contact with the removable layer. However, the sum of A1 and A2 issmaller than A, because step (D10) dividing or cutting may be carriedout by removing away a stripe of the electrically conductive workinglayer, and that stripe always has an area greater than zero. Forexample, (A1+A2) may be in the range of from 80% A to 99.99% A. There isno specific requirement for A1:A2 ratio, for example, A1:A2 ratio mayrange from 1:10 to 10:1.

Additional steps for fabricating a motional sensor may be introduced, orcombined/merged with steps (A10)-(E10). The motional sensor has zero ora minimal response to an acoustic pressure impacting the capacitivemicrophone. In preferred embodiments, the process for fabricating themotional sensor is identical to the process for fabricating the workingcapacitive microphone, with an exception such as one or more openings288 in FIG. 1D. The names of components in the working capacitivemicrophone and counterpart components in the motional sensor are listedin the following table for quick reference.

Components in working Counterpart components in capacitive microphonemotional sensor (identical) working substrate reference substrate planarworking surface planar reference surface primary working directionprimary reference direction electrically conductive electricallyconductive working layer reference layer elevated working area elevatedreference area two divided working layers two divided reference layersfirst electrical working conductor first electrical reference conductorsecond electrical working conductor second electrical referenceconductor first working projection first reference projection secondworking projection second reference projection shortest working distanceDwmin shortest reference distance Drmin working suspensions referencesuspensions working cantilevers reference cantilevers first set ofworking comb fingers first set of reference comb fingers second set ofworking comb fingers second set of reference comb fingers working trenchreference trench working insert reference insert Components in workingcapacitive Counterpart components microphone in motional sensor (notidentical) working membrane reference membrane

Specifically, the following additional steps (a10)-(e10) may beintroduced, and/or combined with above steps (A10)-(E10). Step (a10) isproviding a reference substrate having a planar reference surface,wherein a primary reference direction is defined as a directionperpendicular to the planar reference surface. Step (b10) is depositingat least one removable layer on the planar reference surface. Step (c10)is depositing one electrically conductive reference layer on said atleast one removable layer. Step (d10) is dividing the electricallyconductive reference layer into two divided reference layers, both ofwhich remain in contact with said at least one removable layer and arein parallel with the planar reference surface. Step (e10) is removing oretching away said at least one removable layer to form a motionalsensor.

In preferred embodiments as shown in FIG. 4A, FIG. 4B, and FIG. 4C, Step(A10) and Step (a10) are combined into a step of providing a commonsubstrate for both the working capacitive microphone and the motionalsensor. Step (B10) and Step (b10) are combined as a step of depositingat least one common removable layer for both the working capacitivemicrophone and the motional sensor. Step (C10) and Step (c10) arecombined as a step of depositing a common electrically conductive layeron said at least one common removable layer for both the workingcapacitive microphone and the motional sensor. Step (D10) and Step (d10)are combined as a step of dividing the common electrically conductivelayer into a first electrical working conductor, a second electricalworking conductor, a first electrical reference conductor, and a secondelectrical reference conductor. Step (E10) and Step (e10) are combinedas a step of etching away said at least one common removable layer forboth the working capacitive microphone and the motional sensor.

However, it should be appreciated that steps (D10) dividing and (E10)etching in some embodiments can be carried out so that, in the formedworking capacitive microphone, the first electrical working conductor isfixed relative to the working substrate, and the second electricalworking conductor comprises a working membrane perpendicular to saidprimary working direction that is movable relative to the workingsubstrate. Steps (d10) and (e10) may be carried out in a similar way forthe motional sensor, mutatis mutandis. However, as compared to steps(A10)-(E10), one or more openings are cut on the reference membrane forair ventilation. This is an important difference, or even the onlydifference, between the working capacitive microphone and the motionalsensor.

It should also be appreciated that the left half of FIGS. 4A-4C may beviewed as an illustration for Steps (A10)-(E10) alone, the right half ofFIGS. 4A-4C may be viewed as an illustration for Steps (a10)-(e10)alone, and the entire FIGS. 4A-4C may be viewed as an illustration forfabricating an exemplary microphone of the invention, where Steps(A10)-(E10) and Steps (a10)-(e10) are combined, integrated, or merged.

Referring back to FIGS. 4A-4C, the process may be so carried out that,in the formed working capacitive microphone, the first electricalworking conductor is fixed or stationary relative to the workingsubstrate, and the second electrical working conductor comprises aworking membrane, which is perpendicular to the primary workingdirection and movable relative to the working substrate (up and down).In specific embodiments, step (D10) dividing is carried out so that themovable working membrane is directly or indirectly attached to thesubstrate via three or more working suspensions (not shown) such as fourworking suspensions. The suspension is flexible, and allows the workingmembrane moves up and down. For example, each of the working suspensionsmay be configured to have folded and symmetrical working cantilevers.Step (d10) dividing and step (e10) etching may be carried out in asimilar way, mutatis mutandis.

In preferred embodiments, step (D10) may include cutting a first set ofworking comb fingers (not shown) in the first electrical workingconductor, and cutting a second set of working comb fingers (not shown)around a peripheral region of the movable working membrane. The two setsof working comb fingers are interleaved into each other, and the secondset of working comb fingers are laterally movable relative to the firstset of working comb fingers. In a specific embodiment, the first set ofworking comb fingers and the second set of working comb fingers haveidentical shape and dimension, but they may have a same or differentdistance as measured from the substrate (i.e. a vertical positionalshift). Step (d10) dividing may be carried out in a similar way, mutatismutandis.

For example, step (C10) may be depositing one electrically conductiveworking layer having an elevated working area, and step (D10) may bedividing or cutting the electrically conductive working layer along anedge or a borderline of the elevated area to form two divided layers, sothat each working comb finger has a same working width measured alongthe primary working direction, and the first set of working comb fingersand the second set of working comb fingers have a vertical positionalshift along the primary working direction. In one embodiment, thepositional shift along the primary working direction is one third of theworking/reference width. Step (c10) dividing and step (d10) etching maybe carried out in a similar way, mutatis mutandis.

Step (D10) may be dividing or cutting the movable working membrane insquare shape. Step (D10) may comprise dividing two or more movableworking membranes such as four identical movable working membranesarranged in a 2×2 array configuration above the substrate. Step (d10)dividing may be carried out in a similar way, mutatis mutandis.

There may be 3 different ways for dividing or cutting the electricallyconductive working layer along an edge or a borderline of the elevatedarea to form two divided layers. As shown in FIG. 4D, a first waylabeled as (a) may be completely cutting on the non-elevated side alongthe edge or borderline; a second way labeled as (b) may be cuttingpartially on the non-elevated side and partially on the elevated area,along the edge or borderline; and a third way labeled as (c) may becompletely cutting on the elevated side along the edge or borderline.

It should be appreciated that steps (D10) and (d10) as combined maycomprise cutting m working membrane(s) on said second electrical workingconductor, and cutting n reference membrane(s) on said second electricalreference conductor, wherein m≥1, and n≥1. In preferred embodiments, themotional sensor may have a structure identical to the working capacitivemicrophone, except that one or more openings are cut through thereference membrane for air ventilation. For example, m and n can both be2, and the two working membranes and the two reference membranes arearranged in a 2×2 array configuration above the common substrate (i.e.working substrate combined with reference substrate).

In some embodiments, a step of (A15) may be added, which is etching theplanar working surface of the working substrate to form a workingtrench. Step (C10) depositing may include forming a working insert thatis protruded from the working membrane downward into the working trench.The working insert and the working trench function as a working air flowrestrictor that restricts the flow rate of air flowing in/out of the gapbetween the working membrane and the working substrate in the workingcapacitive microphone. Step (a15) may be added, and carried out in asimilar way to Step (A15), mutatis mutandis. Step (c10) dividing mayalso be carried out in a similar way to Step (C10), mutatis mutandis.

In various embodiments, the first electrical working conductor and thefirst electrical reference conductor are electrically connected to forma common ground to simplify the circuit design.

In various embodiments, the present invention utilizes a referencemoving membrane that can detect substantially only the accelerationsignal. The measured acceleration signal can then be used to cancel outthe component of actual acceleration signal in the total (“gross”)signal as measured by the working capacitive microphone in real-time,through a signal subtraction operation.

FIG. 5A illustrates a more specific embodiment of a lateral microphone200, in which identical conductors 201 and 201 r are fixed relative to acommon substrate 230. Conductor 202 comprises a working membrane 202 mthat is movable relative to the substrate 230, and the primary workingdirection is perpendicular to the working membrane 202 m plane and theplanar face plane of common substrate 230. Reference conductor 202 rcomprises a reference membrane 202 rm that is also movable relative tothe substrate 230, and the primary reference direction is perpendicularto the reference membrane 202 rm plane and the planar face plane ofcommon substrate 230. Working membrane 202 m plane and referencemembrane 202 rm plane may be in parallel with each other. Conductors 202and 202 r are identical except that the reference membrane 202 rm hasless air resistance than the working membrane 202 m. For example,reference membrane 202 rm may have one or more openings 288 thereon forair ventilation, but the working membrane 202 m has no opening.

In exemplary embodiments of the invention, the lateral microphone 200may be a MEMS (Microelectromechanical System) microphone, AKAchip/silicon microphone. Typically, a pressure-sensitive diaphragm isetched directly into a silicon wafer by MEMS processing techniques, andis usually accompanied with integrated preamplifier. For a digital MEMSmicrophone, it may include built in analog-to-digital converter (ADC)circuits on the same CMOS chip making the chip a digital microphone andso more readily integrated with digital products.

In an embodiment as shown in FIG. 5B, capacitive microphone 200 mayinclude a common substrate 230 such as silicon, on which both workingcapacitive microphone 290 and motional sensor 300 are fabricated.Conductor 201/201 r and conductor 202/202 r may be constructed above thesubstrate 230 side-by-side. Alternatively, conductor 201/201 r may besurrounding conductor 202/202 r, as shown in FIG. 5B. In an exemplaryembodiment, conductor 201/201 r is fixed to the substrate 230. On theother hand, conductor 202/202 r may include a membrane that is movablerelative to substrate 230. The primary working/reference direction maybe perpendicular to the membrane plane of 202/202 r. Movable membrane202/202 r may be attached to the substrate 230 via three or more workingsuspensions 202S/202Sr such as four working suspensions 202S/202Srextending from four corners of 202/202 r. Each of the suspension202S/202Sr may comprise folded and symmetrical cantilevers (not shownhere). However, reference membrane 202 r has air ventilation device(s)such as four square openings or holes 288, but working membrane 202 doesnot.

In working capacitive microphone 290, working conductor 201 comprises afirst set of working comb fingers 201 f as shown in FIG. 6 that is fixedto common substrate 230. The movable working membrane in secondconductor 202 comprises a second set of working comb fingers 202 faround the peripheral region of the membrane 202. The two sets of combfingers 201 f and 202 f can be interleaved into each other. The secondset of comb fingers 202 f is movable along the primary direction, whichis perpendicular to the membrane plane 202, relative to the first set ofcomb fingers 201 f. As such, the resistance from air located within thegap between the membrane 202 and the substrate is lowered; for example,25 times lower squeeze film damping. In a preferred embodiment, workingcomb fingers 201 f and comb fingers 202 f have identical shape anddimension. Motional device 300 may be fabricated in a similar way,mutatis mutandis.

As shown in FIG. 7, each comb finger in working capacitive microphone290 has a same width W measured along the primary working direction 210.However, comb fingers 201 f and comb fingers 202 f may have a positionalshift PS along the primary working direction 210, in the absence ofvibration caused by sound wave. For example, the vertical positionalshift PS along direction 210 may be one third of the width W, PS=⅓ W. Inother words, comb fingers 201 f and comb fingers 202 f have an overlapof ⅔W along direction 210, in the absence of vibration caused by soundwave. Motional device 300 may be fabricated in a similar way, mutatismutandis.

Referring to FIGS. 6 and 7, working comb fingers 201 f are fixed to thesubstrate, and working comb fingers 202 f are integrated withmembrane-shaped working membrane 202. When membrane 202 vibrates due tosound wave, fingers 202 f move together with membrane 202. When theoverlap area between two neighboring fingers 201 f and 202 f, orvertical positional shift PS, keeps changing along with this movement,the capacitance between them are changing according. Eventually, acapacitance change signal is detected. In contrast, reference membrane202 (not shown) is designed to vibrate not in response to an impactingsound wave, but mainly or completely in response to acceleration,shaking, or vibration of the microphone 200.

As described in co-pending U.S. application Ser. No. 15/393,831, themovable working membrane 202 may have a shape of square. As shown inFIG. 8A, working capacitive microphone 290 may include one or moremovable working membranes 202. For example, four identical membranes 202can be arranged in a 2×2 array configuration. According to the presentinvention, one or two of the four working membranes 202 can be convertedinto reference membrane(s) 202 r by fabricating or etching one or moreopening(s) 288 thereon, e.g. four square leakage holes 288, for airventilation. FIG. 8B shows a 2×2 array configuration that includes onereference membrane 202 r and three working membranes 202. FIG. 8C andFIG. 8D show two 2×2 array configurations that each includes tworeference membranes 202 r and two working membranes 202.

In some embodiments as shown in FIG. 9, working capacitive microphone290 of the invention comprises one or more such as two air flow workingrestrictors 241 that restrict the flow rate of air that flows in/out ofthe gap between the working membrane 202 and the substrate 230.Restrictors 241 may be designed to decrease the size of a working airchannel 240 for the air to flow in/out of the gap. Alternatively oradditionally, restrictors 241 may increase the length of the working airchannel 240 for the air to flow in/out of the gap. For example,restrictors 241 may comprise a working insert 242 into a working trench243, which not only decreases the size of air channel 240, but alsoincreases the length of the air channel 240. Motional device 300 may befabricated in a similar way, mutatis mutandis.

Air flow working restrictors can help solve the leakage problemassociated with microphone design. In conventional parallel plate designas shown in FIG. 1A, it typically has a couple of tiny holes around theedge in order to let air go through slowly, to keep air pressure balanceon both sides of membrane 101 in low frequency. That is a desiredleakage. However, a large leakage is undesired, because it will let somelow frequency sound wave escape away from membrane vibration easily viathe holes, and will result in a sensitivity drop in low frequency.

In order to prevent this large leakage, a structure is designed andshown in FIG. 9, which illustrates a leakage preventtrench/groove/slot/recess and an insert or a wall. Referring back toFIG. 9, working air flow restrictors 241 may function as a structure forpreventing air leakage in the microphone 200 of the invention. Air flowrestrictor 241 comprises an insert 242 into a groove 243, which not onlydecreases the size of an air channel 240, but also increases the lengthof the air channel 240. In MEMS microphones, a deep slot may be etchedon substrate around the edge of square membrane 202 and then aninserting wall 242 connected to membrane 202 is deposited to form a longand narrow air tube 240, which gives a large acoustic resistance. Thelevel of the air resistance may be controlled by the slot depth etchedon the substrate. The deeper slot, the higher the resistance.

An embodiment of FIG. 8A is shown in FIG. 10, in which 4 single dies arearranged as an array device superimposed with the equivalent circuitthereof. The chip space is more efficiently used and the performance isfurther improved. This array die may have a dimension of 1238×1178 μm,including dicing street 181, and equivalent circuit 182 includingequivalent capacitors 183. Similar embodiments of FIGS. 8B, 8C and 8Dcan be fabricated mutatis mutandis.

FIG. 11 illustrates the configuration of working comb fingers, workingmembrane and working suspensions in accordance with an exemplaryembodiment of the present invention. FIG. 11 shows the basic layout of asingle die, top view of working comb fingers 201 f and 202 f, membrane202 and suspensions 202S. Each side of a square membrane 202 has 60pairs of comb fingers 202 f connected thereto. With 2 μm width of aworking comb finger and 1 μm space between fingers, square membrane 202may need a 380 μm side length. Motional device 300 may be fabricated ina similar way, mutatis mutandis.

Working suspensions 202S may be designed to support working membrane 202so that it can vibrate vertically, i.e. along primary working direction210. It needs to have a suitable spring constant and keeps membrane 202as flat as possible when moving. FIG. 12 (upper panel) shows asuspension spring 202S with folded and symmetrical cantilevers. Thespring 202S contains two folded parts as rotation axis. FIG. 12 (lowerpanel) shows a suspension spring when bending. When the spring 202Sbecomes bending, it looks like “frog legs”, making membrane 202 movevertically and keep flat in a very small corner area. Motional device300 may be fabricated in a similar way, mutatis mutandis.

The process of the invention can be accomplished using surfacemicromachining techniques, bulk micromachining techniques, high aspectratio (HAR) silicon micromachining, and semiconductor processingtechniques etc.

Surface micromachining creates structures on top of a substrate using asuccession of thin film deposition and selective etching. Generally,polysilicon is used as one of the layers and silicon dioxide is used asa sacrificial layer which is removed or etched out to create thenecessary void in the thickness direction. Added layers are generallyvery thin with their size varying from 2-5 micrometers. A main advantageis realizing monolithic microsystems in which the electronic and themechanical components (functions) are built in on the same substrate. Asthe structures are built on top of the substrate and not inside it, thesubstrate's properties are not as important as in bulk micromachining,and the expensive silicon wafers can be replaced by cheaper substrates,such as glass, plastic, PET substrate, or other non-rigid materials. Thesize of the substrates can also be much larger than a silicon wafer.

Complicated components, such as movable parts, are built using asacrificial layer. For example, a suspended cantilever can be built bydepositing and structuring a sacrificial layer, which is thenselectively removed at the locations where the future beams must beattached to the substrate (i.e. the anchor points). The structural layeris then deposited on top of the polymer and structured to define thebeams. Finally, the sacrificial layer is removed to release the beams,using a selective etch process that will not damage the structurallayer. There are many possible combinations of structural/sacrificiallayer. The combination chosen depends on the process. For example it isimportant for the structural layer not to be damaged by the process usedto remove the sacrificial layer.

Bulk micromachining produces structures inside a substrate byselectively etching inside the substrate. Bulk micromachining startswith a silicon wafer or other substrates which is selectively etched,using photolithography to transfer a pattern from a mask to the surface.Bulk micromachining can be performed with wet or dry etches, althoughthe most common etch in silicon is the anisotropic wet etch. This etchtakes advantage of the fact that silicon has a crystal structure, whichmeans its atoms are all arranged periodically in lines and planes.Certain planes have weaker bonds and are more susceptible to etching.The etch results in pits that have angled walls, with the angle being afunction of the crystal orientation of the substrate.

Silicon wafer can be anisotropically wet etched, forming highly regularstructures. Wet etching typically uses alkaline liquid solvents, such aspotassium hydroxide (KOH) or tetramethylammonium hydroxide (TMAH) todissolve silicon which has been left exposed by the photolithographymasking step. These alkali solvents dissolve the silicon in a highlyanisotropic way, with some crystallographic orientations dissolving upto 1000 times faster than others. Such an approach is often used withvery specific crystallographic orientations in the raw silicon toproduce V-shaped grooves. The surface of these grooves can be atomicallysmooth if the etch is carried out correctly, and the dimensions andangles can be precisely defined.

In various embodiments of the invention, the microphone is made using aMEMS manufacturing process. Materials for the process include silicon,polymers, metals, and ceramics etc. Deposition processes can be carriedout using physical deposition and chemical deposition. Patterning can becarried out using lithography, electron beam lithography, ion beamlithography, ion track technology, X-ray lithography, and diamondpatterning. Wet etching can be carried out using isotropic etching,anisotropic etching, HF etching, and electrochemical etching. Dryetching can be carried out using vapor etching (e.g. xenon difluoride)and plasma etching (e.g. sputtering and reactive ion etching (RIE)).

In the following FIGS. 13-36C2, an exemplary process for making thecapacitive microphone of the invention will be illustrated and describedin more details. Six different materials are used in the process:substrate (silicon), thermal oxide (e.g. silicon dioxide), poly silicon,phosphosilicate glass (PSG), silicon nitride, and metal. FIG. 13illustrates the texture representation of these six materials anddiagram of several views appeared in FIGS. 14-36C2. Referring to FIG.13, the working/reference/common substrate such as Silicon has a planarworking/reference surface represented as (X, Y) plane in a 3D coordinatesystem with arbitrary unit (AU). For example, the major tick may be 10UM, and minor tick may be 0.5 UM. Z axis is therefore extending alongthe primary working/reference direction that is perpendicular to the (X,Y) plane. “Top Views along Z axis” in all FIGS. 14-36C2 represent asquare area on (X, Y) plane with a dimension of 50 AU times 50 AU. Thefour corners of the square have coordinates (0, 0), (0, 50), (50, 50)and (50, 0). All top views along Z axis in FIGS. 14-36C2 represent thesquare with four corners (0, 0), (0, 50), (50, 50) and (50, 0).Therefore, all top views have the same size and orientation, despitethat a top view may appear bigger or smaller than another. Plane A1-A2contains two points (0, 48.5, 0) and (48.5, 50, 0), and is in parallelto Z-axis. Plane B1-B2 contains two points (0, 0, 0) and (20, 20, 0),and is in parallel to Z-axis. Plane B2-B3 contains two points (20, 20,0) and (50, 20, 0), and is in parallel to Z-axis. Planes B1-B2-B3 isdefined as a bended plane that starts as plane B1-B2, stops at (20, 20)line, and extends into plane B2-B3. Therefore, cross section view alongplanes B1-B2-B3 in FIG. 13 should be appreciated as cross section viewalong plane B1-B2 as projected on X-Z plane, combined with normalsection view along plane B2-B3. In FIGS. 14-36C2, all cross sectionviews along plane A1-A2 and planes B1-B2-B3 have the same length of 50AU (from X=0 to X=50 AU) along X axis, despite that one cross sectionview may appear bigger or smaller than another.

FIG. 14 shows step (A10)/(a10) of providing a working/referencesubstrate having a planar surface, for fabricating the quarter singledie of the 4-die array as described above. As an embodiment of step(A15)/(a15), FIG. 15 illustrates the first step, deep reactive ionetching (DRIE) on the substrate, whereby a working/reference trench maybe formed. FIG. 16 illustrates the step of (B10)/(b10), depositing atleast one removable layer on the planar surface, e.g. thermal oxidation,in which thermal oxide of 2 μm thickness is deposited on the substrate.FIG. 17 illustrates the step of etching the thermal oxide in FIG. 16,i.e. patterning the thermal oxide layer. FIG. 18 illustrates the step ofpolysilicon deposition, in which a 3 μm, for example, polysilicon layeris deposited. A working/reference insert may be formed and extended inthe trench. FIG. 19 illustrates the step of etching the polysilicon,i.e. patterning the polysilicon layer. FIG. 20 illustrates the step ofsacrificial layer (such as 3 μm PSG) deposition. FIG. 21 illustrates thestep of etching sacrificial layer e.g. PSG as described in FIG. 20, andpatterning PSG to expose the working/reference insert for furtherprocessing. FIG. 22 illustrates the step of isolation layer e.g. 1 μmsilicon nitride deposition, which will isolate functional structure fromthe substrate, and will help in defining comb fingers. FIG. 23illustrates the step of patterning the isolation layer e.g. siliconnitride layer. FIG. 24 illustrates the step of polysilicon e.g. 3 μmdeposition. FIG. 25 illustrates the step of etching polysilicon, andpatterning polysilicon to leave a cavity for membrane support. FIG. 26illustrates the step of sacrificial layer (such as 3 μm PSG) depositionin order to support membrane deposition. FIG. 27 illustrates the step ofetching/patterning PSG, so as to leave area for membrane deposition andpads deposition, and keep the PSG above comb finger to protect combfinger structure. FIG. 28 illustrates the step of polysilicon depositione.g. 1 μm as membrane material.

After the step of FIG. 28, the process can be split into three differentroutes A, B and C. Rout A is shown in FIGS. 29A, 30A, 31A, 32A, 33A1,33A2, 34A1, 34A2, 35A1, 35A2, 36A1 and 36A2. Rout B is shown in FIGS.29B, 30B, 31B, 32B, 33B1, 33B2, 34B1, 34B2, 35B1, 35B2, 36B1 and 36B2.Rout C is shown in FIGS. 29A, 30A, 31A, 32A, 33C1, 33C2, 34C1, 34C2,35C1, 35C2, 36C1 and 36C2.

FIG. 29A illustrates the step of etching additional polysilicon withoutan opening (or membrane hole) formation. FIG. 29B illustrates the stepof etching additional polysilicon with an opening formation. FIG. 30Aand FIG. 30B illustrate the step of depositing metal for pad material,following FIGS. 29A and 29B respectively. FIG. 31A and FIG. 31Billustrate the steps of patterning pads, following FIGS. 30A and 30Brespectively. FIG. 32A and FIG. 32B illustrate the steps of removingremaining sacrificial layer e.g. PSG above polysilicon and preparingcomb fingers fabrication, following FIGS. 31A and 31B respectively.

FIG. 33A1/A2/B1/B2/C1/C2 illustrates the step of patterning/etchingpolysilicon (with no membrane hole for FIG. 33A1/A2, and with a membranehole for FIG. 33B1/B2/C1/C2) to get comb fingers on different heights,i.e. with a vertical positional shift. FIG. 34A1/A2/B1/B2/C1/C2illustrates the step of etching silicon nitride with a same mask (withno membrane hole for FIG. 34A1/A2, and with a membrane hole for FIG.34B1/B2/C1/C2). Keep etching silicon nitride with self-alignment tocancel the effect of tolerance. FIG. 35A1/A2/B1/B2/C1/C2 illustrates thestep of etching back hole or cavity using bulk fabrication (with nomembrane hole for FIG. 35A1/A2, and with a membrane hole for FIG.35B1/B2/C1/C2). FIG. 36A1/A2/B1/B2/C1/C2 illustrates the step ofreleasing: Use wet etching to remove all sacrificial materials orremovable materials to release the microphone product (with no membranehole for FIG. 36A1/A2, and with a membrane hole for FIG. 36B1/B2/C1/C2).

In the foregoing specification, embodiments of the present inventionhave been described with reference to numerous specific details that mayvary from implementation to implementation. The specification anddrawings are, accordingly, to be regarded in an illustrative rather thana restrictive sense. The sole and exclusive indicator of the scope ofthe invention, and what is intended by the applicant to be the scope ofthe invention, is the literal and equivalent scope of the set of claimsthat issue from this application, in the specific form in which suchclaims issue, including any subsequent correction.

1. A process of fabricating a capacitive microphone such as a MEMSmicrophone comprising: (A10) providing a working substrate having aplanar working surface, wherein a primary working direction is definedas a direction perpendicular to the planar working surface; (B10)depositing at least one removable layer on the planar working surface;(C10) depositing one electrically conductive working layer on said atleast one removable layer; (D10) dividing or cutting the oneelectrically conductive working layer into two divided working layers,both of which remain in contact with said at least one removable layerand are parallel with the planar working surface; and (E10) etching awaysaid at least one removable layer to form a working capacitivemicrophone.
 2. The process according to claim 1, wherein the two dividedworking layers become a first electrical working conductor and a secondelectrical working conductor in the working capacitive microphone;wherein a mutual capacitance exists between said two working conductors;wherein the first electrical working conductor has a first workingprojection along said primary working direction on the planar workingsurface, and the second electrical working conductor has a secondworking projection along said primary working direction on the planarworking surface; and wherein the first working projection and the secondworking projection have a shortest working distance Dwmin therebetween,and Dwmin remains greater than zero regardless of that one or two ofsaid two working conductors is (are) impacted by an acoustic pressurealong said primary working direction or not.
 3. The process according toclaim 1, wherein the working substrate comprises silicon, the removablelayer comprises PSG or thermal oxide such as oxides of Si, and said twoworking conductors independently of each other comprise polysilicon,silicon, gold, silver, nickel, aluminum, copper, chromium, titanium,tungsten, or platinum.
 4. The process according to claim 1, whereinsteps (D10) dividing and (E10) etching are carried out so that, in theformed working capacitive microphone, the first electrical workingconductor is fixed relative to the working substrate, and the secondelectrical working conductor comprises a working membrane perpendicularto said primary working direction that is movable relative to theworking substrate.
 5. The process according to claim 4, wherein step(D10) dividing is carried out so that the movable working membrane isattached to the substrate via three or more working suspensions such asfour working suspensions.
 6. The process according to claim 5, whereinstep (D10) is dividing carried out so that each of the workingsuspensions comprises folded and symmetrical working cantilevers.
 7. Theprocess according to claim 4, wherein step (D10) includes cutting afirst set of working comb fingers in the first electrical workingconductor, and cutting a second set of working comb fingers around aperipheral region of the movable working membrane, wherein the two setsof working comb fingers are interleaved into each other, and the secondset of working comb fingers are laterally movable relative to the firstset of working comb fingers.
 8. The process according to claim 7,wherein step (D10) cutting is carried out so that the first set ofworking comb fingers and the second set of working comb fingers haveidentical shape and dimension.
 9. The process according to claim 9,wherein step (C10) is depositing one electrically conductive workinglayer having an elevated working area, and step (D10) is dividing orcutting the electrically conductive working layer along an edge or aborderline of the elevated area to form two divided layers, so that eachworking comb finger has a same working width measured along the primaryworking direction, and the first set of working comb fingers and thesecond set of working comb fingers have a positional shift along theprimary working direction.
 10. The process according to claim 9, whereinthe positional shift along the primary working direction is one third ofsaid width.
 11. The process according to claim 4, wherein step (D10)comprises cutting the movable working membrane in square shape.
 12. Theprocess according to claim 4, wherein step (D10) comprises cutting twoor more movable working membranes such as four identical movable workingmembranes arranged in a 2×2 array configuration above the substrate. 13.The process according to claim 4, further comprising a step of (A15)etching the planar working surface of the substrate to form a workingtrench, wherein step (C10) depositing comprises forming a working insertthat is protruded from the working membrane downward into the workingtrench; wherein the working insert and the working trench function as aworking air flow restrictor that restricts the flow rate of air flowingin/out of the gap between the working membrane and the substrate in themicrophone.
 14. The process according to claim 1, further comprisingforming a motional sensor having zero or a minimal response to anacoustic pressure impacting the capacitive microphone.
 15. The processaccording to claim 14, wherein steps (D10) dividing and (E10) etchingare carried out so that, in the formed working capacitive microphone,the first electrical working conductor is fixed relative to the workingsubstrate, and the second electrical working conductor comprises aworking membrane perpendicular to said primary working direction that ismovable relative to the working substrate, further comprising: (a10)providing a reference substrate having a planar reference surface,wherein a primary reference direction is defined as a directionperpendicular to the planar reference surface; (b10) depositing at leastone removable layer on the planar reference surface; (c10) depositingone electrically conductive reference layer on said at least oneremovable layer; (d10) dividing the electrically conductive referencelayer into two divided reference layers, both of which remain in contactwith said at least one removable layer and are parallel with the planarreference surface; and (e10) etching away said at least one removablelayer to form a motional sensor; wherein steps (d10) dividing and (e10)etching are carried out so that, in the formed motional sensor, thefirst electrical reference conductor is fixed relative to the referencesubstrate, and the second electrical reference conductor comprises areference membrane perpendicular to said primary reference directionthat is movable relative to the reference substrate; and wherein one ormore openings are cut on the reference membrane for air ventilation. 16.The process according to claim 15, wherein step (A10) and Step (a10) arecombined as providing a common substrate for both the working capacitivemicrophone and the motional sensor; step (B10) and Step (b10) arecombined as depositing at least one common removable layer for both theworking capacitive microphone and the motional sensor; step (C10) andStep (c10) are combined as depositing a common electrically conductivelayer on said at least one common removable layer for both the workingcapacitive microphone and the motional sensor, step (D10) and Step (d10)are combined as dividing the common electrically conductive layer intosaid first electrical working conductor, said second electrical workingconductor, said first electrical reference conductor, and said secondelectrical reference conductor, and step (E10) and Step (e10) arecombined as etching away said at least one common removable layer forboth the working capacitive microphone and the motional sensor.
 17. Theprocess according to claim 16, wherein steps (D10) and (d10) as combinedcomprise cutting m working membrane(s) on said second electrical workingconductor, and cutting n reference membrane(s) on said second electricalreference conductor, wherein m≥1, n≥1.
 18. The process according toclaim 17, wherein the motional sensor has a structure identical to theworking capacitive microphone, except that one or more openings are cuton the reference membrane for air ventilation.
 19. The process accordingto claim 18, wherein m=n=2, and the two working membranes and the tworeference membranes are arranged in a 2×2 array configuration above thecommon substrate.
 20. The process according to claim 15, furthercomprising electrically connecting the first electrical workingconductor and the first electrical reference conductor to form a commonground.